Interface Physical Chemistry of Enamels (Part 2)

Abstract

The bubbles that generate during the enamel reaction were studied by TMA. The sample used in the study was a pellet of a mixture of Fe powder and frit powder. The expansion and the shrinkage of a pellet depended on the generation and the breakaway of the bubbles. The influence of cobalt and nickel on generation of the bubbles and its was examined experimentally. (1) The Co-porcelain enamel had a little quantity of bubbles, and the size was uniform. The Ni-porcelain enamel had a large quantity of bubbles, and the size was nonuniform. (2) The bubbles generation existed in the enamel calcination temperature range of 700-900°C. The bubbles of the Co-porcelain enamel were generated at about 740°C. The bubbles of the Ni-porcelain enamel were generated at about 740°C and about 870°C. (3) The generation cause of the bubbles was oxygen as a result of the reduction of superficially present iron oxide. When carbon was included in iron, the bubbles was generated as carbon dioxide, (4) The bubble quantity increased when carbon was included in iron. The Ni-porcelain enamel was more easily influenced by the carbon as compared with Co-porcelain enamel, and generated a large number of bubbles.